This invention pertains to the art of conduit couplings, and more particularly to stab-type couplings for use in conjunction with smooth-walled conduits housing optical fibers and other data carriers such as cables and the like. Of course, it will be appreciated that the invention has broader application to coupling pipes, tubes, hoses, and other articles, and may be advantageously used in other environments and applications.
Fiber-optic cables typically consist of multiple optic fibers or bundles, together with various strengthening and structural members, surrounded by an outer protective dielectric jacket. To further protect a fiber-optic cable, especially when it is installed underground or in other harsh environments, the cable is threaded through lengths of conduit. Suitable plastic conduit includes polyethylene (PE), polyvinyl chloride (PVC), and polybutylene (PB).
Stab-type couplings permit quick and easy connection of pipes, tubes, or other conduit to a piece of equipment or to another conduit. Conduit is simply cut at a right angle to its length to form a transverse end which is inserted or "stabbed" into a coupling body bore. The transverse end of the conduit is forced into the coupling body bore until it abuts a stop member. The coupling includes internal gripping elements that are designed to grip the outer surface of the conduit upon its insertion and prevent its withdrawal. For example, stab-type couplings for fluid conduits are known to include a collet and a tapering sleeve or other element that radially constricts the collet upon the attempted withdrawal of the conduit from the coupling body. Other types of gripping elements include gripper rings, gripper washers, and various spring-type elements.
A problem encountered with known stab-type couplings for conduit is the lack of sufficient conduit gripping force during the initial stages of attempted conduit withdrawal from the coupling body. The gripping elements in known couplings do not sufficiently grip the conduit to halt its movement until after the conduit is pulled a certain distance out of the coupling body to actuate the gripping elements. This freedom of movement results in an unstable connection between the coupling and the conduit and ultimately leads to failed connections.
Various stab-type couplings have incorporated means for preloading or "setting-up" the gripping elements thereof so that outward axial movement of a conduit is limited, even during the initial stages thereof. This requires some gripping element that initially passively grips the conduit, without the need for axial outward motion of conduit. Upon axial outward movement of the conduit, the passive gripping element moves with the conduit and ensures actuation of one or more active gripping elements, such as a collet. While some such couplings, such as that set forth in U.S. Pat. No. 4,229,025 and U.S. Pat. No. 5,150,925 have been found to be effective in fluid handling applications, known fluid couplings are not suitable for use in conjunction with optical fiber and other communications conduit. In particular, these couplings include stiffeners, pistons, plural O-ring seals, and other parts in the coupling body to form an effective fluid-tight seal. Certain of these elements do not significantly interfere with fluid flow, but do interfere with the threading of optical fiber bundles, copper cables, and other data carriers through the conduit and associated coupling as is required for communications applications. Also, there is no elevated internal fluid pressure in a fiber-optic bundle conduit as might be encountered in hydraulic lines and the like. Thus, no seals are required against such internal pressure. Certain known fluid couplings for hydraulic, pneumatic, and other such applications actually rely upon the internal fluid pressure to actuate gripping elements in a piston-like fashion. Of course, such couplings are not suitable for use with conduit of the type used to house optical fiber bundles and the like. Further, each element inside of a coupling increases its cost, both in terms of the parts and the assembly.
Gripping teeth or other elements that grip the outer wall of a conduit even when no axial outward movement of the conduit is present must engage the outer wall of the conduit in an interference fit. However, another drawback associated with known couplings including such gripping elements is that the gripping elements interfere with the proper insertion of a conduit into the coupling. Unless a conduit is fully and properly inserted into a coupling, it will not be effectively retained therein. For example, certain pre-loaded gripping elements engage an entire circumferential region of a conduit. This renders conduit insertion more difficult, but does not provide significant gripping advantages.
Accordingly, it is desirable to develop a new and improved coupling for fiber-optic elements which overcomes the foregoing deficiencies and others while providing better and more advantageous overall results.